Direct growth of carbon nanotubes atom by atom during field emission
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1204-K01-01
Direct Growth of Carbon Nanotubes Atom by Atom During Field Emission Catherine Journet1, Mickaël Marchand1, Jean-Michel Benoit1, Boris I. Yakobson2 and Stephen T. Purcell1 1
Laboratoire de Physique de la Matière Condensée et Nanostructures, Université Lyon1; CNRS, UMR 5586, Domaine Scientifique de la Doua, F-69622 Villeurbanne cedex, France 2
Rice University, Smalley Institute, ME&MS Department, MS 321, Houston, TX 77005-1892, U.S.A. ABSTRACT We have designed a field emission microscope (FEM) coupled to a chemical vapor deposition (CVD) reactor in order to observe directly the growths of individual carbon nanotubes (CNTs) from the nucleation stage. Catalyst metals are first deposited in situ on a sharp metallic tip during direct FEM imaging and formed into nanoparticles by dewetting. CNTs are then grown directly on these nanoparticles by CVD in acetylene or other hydrocarbon gases at appropriate temperatures (600-900°C). The FEM patterns are formed by electrons emitted from individual CNT caps. The videos are analyzed to extract the growth rates and models. In situ field emission I/V measurements are also performed. The most interesting new discovery is that the CNTs often rotate axially during growth, thus strongly supporting a recently proposed model of 'screw-dislocation-like' (SDL) mechanism [1]. The event is not rare as four rotating CNT growths versus six non-rotating growths were observed. In one case the CNT rotated quite uniformly ~180 times during its 11 min growth. This observation should aid researchers to better understand and control the growth of SWNTs.
INTRODUCTION The key issue for realizing the potential of CNTs has always been, and still remains, a better control of CNT growth [2,3]. Measurement techniques, models and control are needed at the atomic scale as this is the size of the critical growth zone. Simulations suggest such models [4,5] but the many possibilities they open must be guided by experiment. Though important progress is now being made by growing CNTs in transmission electron microscopes (TEM) [6,7,8,9], they do not yet show how individual atoms integrate into a growing CNT. Drawing on older work for crystals [10], Ding, et al. [1] have recently proposed that atoms may integrate repetitively around the edges of growing single wall nanotubes (SWNTs) by a ‘screwdislocation-like’ (SDL) mechanism. Such a mechanism is attractive because it points towards controlled growth as currently done in bulk single crystal growth and molecular beam epitaxy and connects the growth speed to helicity because it determines the number of carbon acceptor sites at the growing edge. However to test this theory and find the experimental conditions over which it is applicable, an experimental method that can measure growth with an atomic
resolution is needed. In this article we show that field emission permits such resolution and we use it to show that the SDL mechanism in certain conditions can govern SWNT growth. EXPERIMENT We have implemented a new and original method for observing the g
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